The invention relates to the generation of a cosine wave reference for the generation of thyristor triggering pulses in static power converters. The cosine wave crossing timing principle is generally known in the art of static power converters (see "Static Power Frequency Changes" by Gyugyi and Pelly, John Wiley Edition 1976, pp. 279-298). The known advantage of using a cosine wave as a time reference is that it introduces a linear function between the cosine voltage and the output voltage of the thyristor bridge. It is known to modify a sine wave reference received from the line so as to generate a cosine wave which is compared with a variable DC control voltage for the determination of the thyristor conduction angle. Several problems have been met in the prior art by manipulating the inputted sine wave in a particular manner. Thus, in U.S. Pat. No. 3,983,495 the object is to obtain a sine wave to cosine wave conversion which is insensitive to frequency.
An object of the present invention is to successively generate, from a common phase line sine wave, a series of cosine waves sequentially associated with the successive phase lines, each cosine wave having the required phase shift in the sequence of firing the thyristors, such firing being effected under a single and common comparator circuit.